Stereotactic arrhythmia radioablation (STAR) has emerged as a salvage treatment for patients with ventricular tachycardia, and the MR-linacs offer MRI-guidance during such treatment. However, available workflows on MR-linacs are not yet optimized and characterized dedicatedly to perform heart radiotherapy due to a lack of realistic MRI-compatible cardiac phantoms suitable for real-time dosimetry. This work introduces a newly designed, deformable, and MRI-compatible cardiac phantom with real-time and multi-point dosimetric capabilities, characterizes its MRI properties and mechanical behavior, and showcases its use for MR-linac end-to-end workflowtesting. This cardiac phantom (IBA QUASAR, London, Ontario, Canada) is composed of a deformable heart model - representing the left and right ventricles - with integrated Plastic Scintillation Detectors (Medscint, Quebec, Quebec, Canada) (PSDs), a sectionfilled with contrast solution, and a piston compatible with the motor of the QUASARTM MRI4D motion phantom. We determined its T1 and T2 values by acquiring gold standard inversion recovery and spin echo sequences. We evaluated its 2D deformation and mechanical behavior by performing an MRI-based analysis inspired by dynamic mechanical analysis. We evaluated its 3D deformation and mechanical behavior by acquiring 3D scans at different motor positions, and by applying deformable image registration. We evaluated the reliability of the PSD measurements by testing the repeatability, linearity, and dose rate dependency of their measured dose on a 1.5 T Unity MR-linac (Elekta AB, Stockholm, Sweden). We evaluated the dosimetric impact of motion and motion mitigation on the dose measured by the PSDs by delivering a STAR plan in different cases: static, motion (cardiorespiratory or cardiac motion), and motion with gating (MR-linac clinical workflow). On average, T1 values were T1constrast_solution = 1130 44 ms, T1left_ventricle's_wall = 763 76 ms, and T1right_ventricle's_wall = 775 69 ms, and T2 values were T2constrast_solution = 155 16 ms, T2left_ventricle's_wall = 49 12 ms, and T2right_ventricle's_wall = 185 35 ms. For the 2D deformation, no phase lag of deformation (i.e., ventricular area) with respect to the piston motion and no hysteresis behavior were observed. For the 2D and 3D deformation, linear relationships between piston positions and ventricular areas or volumes of interest were observed (R2 = 0.99 and R2 = 1.0, respectively). For the 3D deformation, negligible differences between volumes before and after PSDs integration were obtained (largest absolute percentage difference of 1.1%). The maximum deformation of the heart model was 5 mm. For the dosimetric capabilities, the reliability of the PSD measurements was shown (repeatability: coefficient of variation 0.31%, linearity: R2 = 1.0, dose rate dependency: coefficient of variation 0.72%). Dose rates measured by the PSDs over time during STAR delivery were fluctuating in phase with the motion pattern. Percentage errors on cumulative doses with respect to static cases when cardiorespiratory or cardiac motion were applied were, respectively, up to -28.6% and -0.7% in motion cases, and up to -3.1% and 0.8% in gatingcases. This deformable and MRI-compatible cardiac phantom has good MRI contrast, and its heart model exhibits elastic behavior. Its integrated PSDs offer real-time and multi-point dose measurements, and their reliability was demonstrated. We successfully showed that this cardiac phantom enables end-to-end testing for heart radiotherapy onMR-linacs.

BackgroundCardiac stereotactic body radiotherapy (CSBRT) is a promising new option for patients with refractory arrhythmias, but complex combined cardiopulmonary motion poses a challenge for precise CSBRT treatment. At present, the dosimetric effects of cardiopulmonary motion on the actual delivery of CSBRT are still unclear, which may deter its widespread clinical application. This study aimed to evaluate the dosimetric effects of complex cardiorespiratory motion during CSBRT and explore the dosimetric advantages of respiratory gating.MethodsA dynamic cardiac phantom was used to simulate different patterns of cardiac pulsation, respiratory motion, and cardiorespiratory motion. Radiochromic film was used to measure the dose, with radiation doses measured for both free-breathing and respiratory-gated CSBRT across various motion pattern groups. The dose measured with a static phantom served as the reference. Subsequently, the measured dose distributions were compared with that of the reference to evaluate the dose difference, gamma passing rate (GPR), isodose width (IDW), and penumbra width.ResultsIncreased cardiorespiratory motion in CSBRT led to a decreased GPR (3%/2 mm), reduced 90% and 80% IDWs, and a broadened penumbra. Dose-blurring and interplay effects were also observed. Under free-breathing delivery, the mean GPR at the 3%/2 mm criterion was 42.6% in the large‑motion group. Compared with free-breathing delivery, respiratory‑gated delivery increased the mean GPR for the 3%/2 mm criterion by 19.4%. Respiratory amplitude had the greatest dosimetric effect, while heart rate, respiratory cycle, and onset phase had minimal effects.ConclusionsCardiorespiratory motion introduced dose uncertainties and interplay effects during CSBRT, leading to dose variations in the target and non-uniform dose distributions in the peripheral region surrounding the target, including cold and hot spots. The adoption of gating techniques substantially improved dose precision in CSBRT, effectively mitigating dose uncertainties associated with cardiorespiratory motion. Our findings highlight the importance of implementing respiratory motion management techniques to enhance the effectiveness and safety of CSBRT.

Impact of heart rate on coronary artery stenosis grading accuracy using deep learning-based fast kV-switching CT: A phantom study.

PurposeTo provide insight into appearance of local distortion as a pitfall and to assess performance of MLEM reconstruction in presence of a high‐contrast object or hot spot and to quantify extent of involvement, specifically in myocardial perfusion imaging.MethodsA checkerboard image is reconstructed with MLEM with and without the presence of a high‐contrast region or hot spot to demonstrate pattern of distortion in near and distant locations around it. Then, a cardiac NCAT phantom is constructed without (“control”) and with a nearby hot spot or highly‐intense object (as lung lesion close to lateral wall of LV). An in‐house MLEM algorithm is implemented and utilized for reconstruction. Images are analyzed by creating error images and profile plotting.FindingsPattern of distortion on a checkerboard image is like a two diagonal bands of the same width of the spot crossing perpendicularly. Higher relative intensity (5:1 vs. 2:1) results in more distortion both in extent and severity. Tomographic image of control NCAT phantom reveals an almost uniform intensity in lateral wall. However, as relative intensity of spot increases, distortion worsens. Circumferential curves of all walls are almost superimposed except for the wall close to object (or lateral wall of the LV).ConclusionPresence of a hot spot or object creates distortion its own periphery during MLEM reconstruction. The object‐of‐interest is influenced if located in that region. Degree of distortion depends on relative intensity of hot object to background. Likewise, an artifactual defect is created in LV wall in myocardial perfusion imaging.

Bioheat transfer is the study of heat transport applied in anatomy and physiology, and it is a critical tool when analyzing thermal exposures and various treatments and diagnostic methods. Blood flow significantly impacts heat transfer throughout the body, facilitating the diffusion of heat. Several models have been developed to quantify bioheat transfer and the effect of blood flow through tissue for many biological functions and medical procedures, one of which is radiofrequency ablation for cardiac arrhythmia. While some previous studies suggested that the effect of tissue perfusion may be critical only for highly vascularized organs, such as the liver, other studies concluded that the convective effect at the endocardium is a more significant factor than inner tissue perfusion. Nevertheless, significant improvements to models and assumptions are still required, as success rates for this procedure remain low for various arrhythmia types. In the effort to quantitatively assess the impact of considering (or not) the effect of tissue perfusion when modeling thermal ablation, this work focuses on studying the effects of perfusion using a tissue-mimicking phantom both experimentally and numerically. We conducted a parametric study of the flow rate through piping system embedded inside the tissue-mimicking phantom and analyzed the transient thermal profile at different locations and depths in the phantom. This study used a physical experimental setup and its homologous computational fluid dynamics model, with material properties and conditions for the numerical simulations from previous research. The numerical results were compared with the computational results. The findings of this study supported that perfusion impacts the transient thermal profile and that further research is needed to expand this foundation into clinically relevant experimentation.Clinical Relevance- This paper investigates the effect of tissue perfusion in thermal ablation modeling of cardiac tissue.

1402 Novel customized dynamic cardiac phantom for complete end-to-end-testing of STereotactic Arrhythmia Radioablation (STAR

Two-dimensional (2D) cine imaging is essential in routine clinical cardiac MR (CMR) exams for assessing cardiac structure and function. Traditional cine imaging requires patients to hold their breath for extended periods and maintain consistent heartbeats for optimal image quality, which can be challenging for those with impaired breath-holding capacity or irregular heart rhythms. This study aims to systematically assess the performance of a deep learning-based reconstruction (Sonic DL Cine, GE HealthCare, Waukesha, WI, USA) for accelerated cardiac cine acquisition. Multiple retrospective experiments were designed and conducted to comprehensively evaluate the technique using data from an MR-dedicated extended cardiac torso anatomical phantom (digital phantom) and healthy volunteers on different cardiac planes. Image quality, spatiotemporal sharpness, and biventricular cardiac function were qualitatively and quantitatively compared between Sonic DL Cine-reconstructed images with various accelerations (4-fold to 12-fold) and fully sampled reference images. Both digital phantom and in vivo experiments demonstrate that Sonic DL Cine can accelerate cine acquisitions by up to 12-fold while preserving comparable SNR, contrast, and spatiotemporal sharpness to fully sampled reference images. Measurements of cardiac function metrics indicate that function measurements from Sonic DL Cine-reconstructed images align well with those from fully sampled reference images. In conclusion, this study demonstrates that Sonic DL Cine is able to reconstruct highly under-sampled (up to 12-fold acceleration) cine datasets while preserving SNR, contrast, spatiotemporal sharpness, and quantification accuracy for cardiac function measurements. It also provides a feasible approach for thoroughly evaluating the deep learning-based method.

Patient motion, particularly due to respiration, often introduces image distortions that compromise diagnostic accuracy in myocardial perfusion single-photon emission computed tomography (SPECT). To address this issue, we developed a novel respiratory motion reduction block (RRB) designed to minimize the respiratory motion of the heart. This study aims to evaluate the impact of the cardiac-centered with RRB (CCRRB) orbit, achieved using the RRB, on myocardial perfusion SPECT image quality. SPECT acquisition of a cardiac phantom was performed at the circular, neighboring elliptical (NE), and CCRRB orbits. The CCRRB orbit was achieved with RRB placed in front of the phantom based on the NE orbit. Count profile curves of the lesion and uniform slice images were obtained from the circumferential profile. Lesion contrast, normal accumulation uniformity, and count distortion were calculated from the circumferential profiles. Full width at half maximum (FWHM) was measured in the lateral, anterior, septal, and inferior walls of the myocardium, and both the mean and standard deviation (SD) were calculated. The lesion contrast was the highest in the NE orbit, slightly lower in the CCRRB orbit, and remarkably lower in the circular orbit than in the NE orbit. The uniformity and count distortion were superior for the CCRRB orbits. The SD of FWHM was greater in the circular and NE orbits. The CCRRB orbit effectively improves uniformity in SPECT imaging, preserving lesion contrast and spatial resolution. The CCRRB orbit provides a practical, accessible approach for enhancing image quality in clinical settings.

18F-sodium fluoride (18F-NaF) positron emission tomography (PET) detects active microcalcification and predicts adverse outcomes including bioprosthetic valve deterioration. However, measuring small areas of 18F-NaF uptake within moving structures remains challenging, requiring further optimization. We developed a representative cardiac phantom to optimize 18F-NaF imaging of bioprosthetic valves. We placed a bioprosthetic valve with two pockets sutured to the leaflets mimicking valvular lesions and a subvalvular ring mimicking the valve remnant into the phantom and injected each with 18F-radionuclide (1 μCi pockets, 4 μCi ring). We injected the cardiac chambers with iohexol and 18F-radionuclide (0.176 mCi) for background activity. PET and computed tomography (CT) images were acquired using a Siemens Biograph Vision high-resolution digital PET/CT scanner. We analysed target-to-background ratio (TBR) and signal-to-noise ratio (SNR) and subjective measures of image quality. We compared results with a human case of transcatheter aortic valve replacement. Initially the SNR and TBR in the phantom greatly exceeded those from human imaging. We reduced the scan duration used for reconstruction to 30 and 15 s, achieving comparable results (30 s vs. 15 s vs. patient: SNR 45.6 vs. 13.9 vs. 44.3, TBRmax 6.5 vs. 5.4 vs. 4.1, noise 10.2% vs. 8.8% vs. 12.0%). With motion correction, SNR and image quality improved in the phantom (30 s 135.8 vs. 45.6, 15 s 32.9 vs. 13.9) but remained similar in the human case (47.3 vs. 44.3). A cardiac phantom can mimic clinical 18F-NaF valve bioprosthesis imaging, providing an opportunity to explore acquisition, reconstruction, and post-processing of 18F-NaF PET/CT for small mobile cardiac structures.

Introduction. Monte Carlo simulation codes simulating medical imaging nuclear detectors (SIMIND) are notable tools used to model nuclear medicine experiments.This study aimed to confirm the usability of SIMIND as an alternative method for nuclear medicine experiments with a cardiac phantom HL, simulating human body structures, by comparing the actual experiment data.Methods. A cardiac phantom HL that simulates myocardial scintigraphy using123I-meta-iodobenzylguanidine was developed, and single-photon emission computed tomography/computed tomography imaging was performed using Discovery NM/CT 670 scanner. Aside from the main-energy window(159 keV ± 10%), additional windows were set on the low(137.5 keV ± 4% ) and high(180.5 keV ± 3%)-energy sides. The simulations were performed under the same conditions as the actual experiments. Regions of interest (ROIs) were set in each organ part of the experiments and simulated data, and a polar map for the myocardial part was developed. The mean, maximum (max), and minimum (min) counts within each ROI, as well as the relative errors of each segment in the polar map, were calculated to evaluate the accuracy of the simulation.Results. Overall, the results were favorable with relative errors of <10% except in some areas based on the data from the main-energy window and postreconstruction. On the other hand, relative errors of >10% were found in both the low and high subenergy windows. The smallest error occurred when assessing using mean values within the ROIs. The relative error was high at the cardiac base in the polar map evaluation; however, it remained <10% from the mid to apical heart sections.Conclusion. SIMIND is considered an alternative method for nuclear medicine experiments using a myocardial phantom HL that closely resembles human body structures. However, caution is warranted as accuracy may decrease under specific conditions.

Stereotactic arrythmia radioablation (STAR) is a noninvasive technique to treat ventricular tachycardia (VT). Management of cardiorespiratory motion plays an essential role in VT-STAR treatments to improve treatment outcomes by reducing positional uncertainties and increasing dose conformality. Use of an electrocardiogram (ECG) signal, acquired in real-time, as a surrogate to gate the beam has the potential to fulfil that intent. To investigate the gated delivery of volumetric-modulated arc therapy (VMAT) for STAR on a TrueBeam linear accelerator (linac) using a real-time acquired ECG signal and a dynamic cardiac phantom. Dosimetric characteristics of a 6 MV flattening filter free (FFF) beam from a Varian TrueBeam linac were initially evaluated under high-frequency gating scenarios relevant to cardiac rhythms with respect to dose linearity, beam output, and energy quality. A microcontroller board was used to interface and gate the linac, sending a beam on/off signal. For real-time cardiac gated measurements, an AD8232 Heart Monitor board was used to acquire the ECG signal and synchronize the VMAT delivery to an ArcCHECK detector to a specific phase of the cardiac cycle. Gated dose distributions were compared against those acquired for a non-gated delivery mode. An in-house dynamic cardiac phantom was developed to simulate cardiorespiratory motion that correlates target position with the signal to gate the beam. Measured dose distributions using gafchromic film were also compared against the static (reference) mode in different scenarios with and without gating. Maximum difference in dose per monitor unit (MU) was found to be no greater than 1% as compared to static mode with variation in the chamber response within 0.2% in the range of 50 MUs to 200 MUs. Maximum percentage differences for the beam output and beam qualiy index (TPR20,10) between gated and non-gated modes were 0.91% and -0.44%, respectively. Comparison of delivered dose distributions for the VMAT plan without gating versus ECG synchronized gating modes provided a passing rate 98% for the gamma analysis with 1% relative dose difference, 1mm distance-to-agreement criteria. For the synchronization of dose delivery with target position, passing rates were 98%, 97%, and 99% for the axial, coronal, and sagittal planes, respectively, when gating the beam based on target position for cardiac motion only, for 3%, 3mm tolerance as compared to static mode. Without gating the beam, passing rates of the respective plans are 97%, 94%, and 99% for the cardiac motion only, and 67%, 57%, and 55% when including respiratory component of motion. A 6 MV-FFF TrueBeam is stable for performing gating in STAR under high-frequency gate windows within typical cardiac cycles. Agreement between measured dose distributions for a VMAT plan in static and ECG-synchronized deliveries and between static and target-position gated modes shows that the proposed methodology is feasible and can be implemented on a TrueBeam platform.

In Gd-EOB-DTPA-enhanced MRI, cardiac pulsation artifacts in the left lobe often hinder diagnosis, the image quality need to improve. This study aimed to reduce cardiac pulsation artifacts in Gd-EOB-DTPA-enhanced three-dimensional (3D) T1-weighted turbo-field echo (3D-T1TFE) using compressed sensitivity encoding (CS).For phantom evaluation, the cardiac phantom was manually operated using a metronome-synchronized apparatus, comprising a bag-valve mask, a breathing circuit, and a Jackson-Rees system. Transverse images of a liver phantom were acquired using enhanced T1 high-resolution isotropic volumetric excitation with CS (CS-eTHRIVE) and sensitivity encoding (S-eTHRIVE). For evaluation, images obtained during cardiac phantom operation were subtracted from those obtained when the phantom was stationary. Standard deviation (SD) of the difference images was used as the evaluation metric, and assessments were conducted based on changes in heart rate and TFE factor. For clinical image evaluation, artifacts in hepatobiliary phase images acquired 15min after Gd-EOB-DTPA injection in the order of S-eTHRIVE and CS-eTHRIVE were visually evaluated at four levels. In heart-rate evaluation (40, 60, and 80 beats/min), CS-eTHRIVE revealed significantly lower SD values compared to S-eTHRIVE across all heart rates (P < 0.01), with no significant differences between heart rates. For TFE factor evaluation, CS-eTHRIVE with a factor of 35 exhibited the lowest SD, which was significantly different from all other groups (P < 0.01). In clinical image evaluation, CS-eTHRIVE achieved higher visual scores (mean ± SD: 3.72 ± 0.46) compared with S-eTHRIVE (2.72 ± 0.98, P < 0.01).CS reduced pulsation artifacts in Gd-EOB-DTPA-enhanced 3D-T1TFE.

Cardiac ablation (CA) is an interventional electrophysiological procedure used to disrupt arrhythmic substrates in the myocardium by inducing localized scarring. Current CA training relies on the master–apprentice model. In different fields of medicine including CA, virtual and physical simulators have proven to enhance, and even outperform, conventional training modalities while providing a risk-free learning environment. Despite the benefits, high costs and operational difficulties limit the widespread use of interventional simulators. Our previous research introduced a low-cost CA simulator using a 3D-printed biatrial cardiac model, successfully recording ten ablation lesions on the phantom myocardium. In this work, we present and evaluate an enhanced version: compared to the previous version, the cardiac phantom’s electrical behavior and ablation settings were optimized to produce consistent lesions, while 3D-printed components improved the haptic and radiographic properties of the simulator. Seven cardiologists compared the experimental simulator’s performance to the leading commercial system from Heartroid in a 24-question survey on a 5-point Likert scale. The four following areas of fidelity were considered: catheter entry, anatomical correctness, radiographic appearance, and mapping and ablation. The experimental simulator significantly outperformed the commercial system (p &lt; 0.01), particularly in radiographic appearance (p &lt; 0.01). The results show the potential for the experimental simulator in routine CA training.

ObjectiveMyocardial blood flow (MBF) assessment can provide incremental diagnostic and prognostic information and thus the validation of dynamic SPECT is of high importance. We recently developed a novel cardiac phantom for dynamic SPECT validation and compared its performance against the GE Discovery NM 530c. We now report its use for validation of a new hybrid SPECT/CT System featuring advanced cadmium zinc telluride (CZT) technology in a ring array detector design (StarGuide™, GE HealthCare).MethodsOur recently developed cardiac phantom with injected technetium-99m radiotracer was used to create physiological time activity curves (TACs) for the left ventricular (LV) cavity and the myocardium. The TACs allow the calculation of uptake rate (K1) and MBF. The StarGuide system was used to acquire and process the TACs, and these were compared to the TACs produced by the phantom and its mathematical model. Fifteen (15) experiments with different doses representing various MBF values were conducted, and a standard statistic tool was applied for significance.ResultsThe TACs produced by the StarGuide system had a significant correlation (p < 0.001) with the reference TACs generated by the phantom both for the LV (r = 0.94) and for the myocardium (r = 0.89). The calculated MBF difference between the system and the phantom was 0.14 ± 0.16 ml/min/g and the average relative absolute difference was 13.2 ± 8.1%. A coefficient of variance of ≤ 11% was observed for all MBF subranges. The regional uptake rate values were similar to the global one with a maximum difference of 5%.ConclusionsOur newly developed dynamic cardiac phantom was used for validation of the dynamic hybrid SPECT/CT CZT-based system (StarGuide™, GE). The accuracy and precision of the system for assessing MBF values were high. The new StarGuide system can reliably perform dynamic SPECT acquisitions over a wide range of myocardial perfusion flow rates.

To investigate the effect of heart rate and virtual monoenergetic image (VMI) on coronary stent imaging in dual-source photon-counting detector computed tomography (PCD-CT). A dynamic cardiac phantom was used to vary the heart rate at 50 beats per minute (bpm), 70bpm, and 90bpm. Five types of stents (4.0mm, 3.5mm, 3.0mm, 2.75mm, and 2.5mm diameter) were scanned at three different locations and reconstructed VMI at 70keV. In addition, 50% stenosis was assessed for 3.0mm and 4.0mm stents. To assess in-stent stenosis, 40keV, 70keV, and 100keV images were compared. Measurable lumen and contrast to noise ratio (CNR) from lumen to stenosis were evaluated quantitatively. A-4-point scale was used for the qualitative image quality of in-stent stenosis. The measurable lumen had no significant differences among heart rates in patent stents (p = 0.55). In-stent stenosis, the residual lumen was significantly larger in 40keV [27.5% (20.8-32.3%)] than in 70keV [11.5% (10.0-23.0%), p < 0.05] and 100keV [0% (0-5.2%), p < 0.05]. The CNR was higher in 40keV [12.5 (7.5-18.2)] than in 70keV [5.3 (2.9-7.7), p < 0.05] and 100keV [1.3 (0.5-2.7), p < 0.05]. The image quality was better in 40keV (3.4 ± 0.7) than in 70keV [(2.6 ± 0.8), p < 0.05] and 100keV [(1.3 ± 0.4), p < 0.05]. Dual-source PCD-CT maintains a measurable lumen even at high heart rates. Adjusting the VMI can be helpful in visualizing the in-stent stenosis.

Cardiac applications in radiation therapy are rapidly expanding including magnetic resonance guided radiation therapy (MRgRT) for real-time gating for targeting and avoidance near the heart or treating ventricular tachycardia (VT). This work describes the development and implementation of a novel multi-modality and magnetic resonance (MR)-compatible cardiac phantom. The patient-informed 3D model was derived from manual contouring of a contrast-enhanced Coronary Computed Tomography Angiography scan, exported as a Stereolithography model, then post-processed to simulate female heart with an average volume. The model was 3D-printed using Elastic50A to provide MR contrast to water background. Two rigid acrylic modules containing cardiac structures were designed and assembled, retrofitting to an MR-safe programmable motor to supply cardiac and respiratory motion in superior-inferior directions. One module contained a cavity for an ion chamber (IC), and the other was equipped with multiple interchangeable cavities for plastic scintillation detectors (PSDs). Images were acquired on a 0.35 T MR-linac for validation of phantom geometry, motion, and simulated online treatment planning and delivery. Three motion profiles were prescribed: patient-derived cardiac (sine waveform, 4.3mm peak-to-peak, 60 beats/min), respiratory (cos4 waveform, 30mm peak-to-peak, 12 breaths/min), and a superposition of cardiac (sine waveform, 4mm peak-to-peak, 70 beats/min) and respiratory (cos4 waveform, 24mm peak-to-peak, 12 breaths/min). The amplitude of the motion profiles was evaluated from sagittal cine images at eight frames/s with a resolution of 2.4mm × 2.4mm. Gated dosimetry experiments were performed using the two module configurations for calculating dose relative to stationary. A CT-based VT treatment plan was delivered twice under cone-beam CT guidance and cumulative stationary doses to multi-point PSDs were evaluated. No artifacts were observed on any images acquired during phantom operation. Phantom excursions measured 49.3±25.8%/66.9±14.0%, 97.0±2.2%/96.4±1.7%, and 90.4±4.8%/89.3±3.5% of prescription for cardiac, respiratory, and cardio-respiratory motion profiles for the 2-chamber (PSD) and 12-substructure (IC) phantom modules respectively. In the gated experiments, the cumulative dose was<2% from expected using the IC module. Real-time dose measured for the PSDs at 10Hz acquisition rate demonstrated the ability to detect the dosimetric consequences of cardiac, respiratory, and cardio-respiratory motion when sampling of different locations during a single delivery, and the stability of our phantom dosimetric results over repeated cycles for the high dose and high gradient regions. For the VT delivery, high dose PSD was<1% from expected (5-6 cGy deviation of 5.9Gy/fraction) and high gradient/low dose regions had deviations<3.6% (6.3 cGy less than expected 1.73Gy/fraction). A novel multi-modality modular heart phantom was designed, constructed, and used for gated radiotherapy experiments on a 0.35 T MR-linac. Our phantom was capable of mimicking cardiac, cardio-respiratory, and respiratory motion while performing dosimetric evaluations of gated procedures using IC and PSD configurations. Time-resolved PSDs with small sensitive volumes appear promising for low-amplitude/high-frequency motion and multi-point data acquisition for advanced dosimetric capabilities. Illustrating VT planning and delivery further expands our phantom to address the unmet needs of cardiac applications in radiotherapy.

This study aims to evaluate the performance of dual-energy window (DEW) and triple-energy window (TEW) scatter correction methods in cardiac SPECT imaging with technetium-99m (Tc-99m) and thallium-201 (Tl-201) radioisotopes. The SIMIND Monte Carlo program was used to simulate the imaging system and produce the required projections. Two phantoms, including the simple cardiac phantom and the NCAT phantom, were used to evaluate the scatter correction methods. The simulations were repeated 5 times for each phantom and finally, the mean values obtained from these 5 tests were used in the analysis of the results. The obtained results from this study show that in the case of both investigated phantoms, the use of correction methods leads to improve the contrast of the images obtained from Tc-99m and Tl-201 radioisotopes. In the case of the simple cardiac phantom, the use of DEW and TEW correction methods leads to a relative increase in image contrast of about 23.88% and 12.23% for 99mTc radioisotope and about 29.19% and 20.98% for 201Tl radioisotope, respectively. This relative increase in the case of the NCAT phantom is about 22.48% and 19.43% for 99mTc radioisotope and about 27.74% and 24.74% for 201Tl radioisotope, respectively. According to the obtained results, despite the higher contrast of the noncorrected images of 99mTc radioisotope, the relative increase in contrast of the corrected images of 201Tl radioisotope is more than that of 99mTc radioisotope. Furthermore, for both radioisotopes, the relative increase related to the DEW method is higher than the TEW method.

Background: The electrodes of implantable cardiac devices (ICDs) may cause significant problems in cardiac computed tomography (CT) because they are a source of artifacts that obscure surrounding structures and possible pathology. There are a few million patients currently with ICDs, and some of these patients will require cardiac imaging due to coronary artery disease or problems with ICDs. Modern CT scanners can reduce some of the metal artifacts because of MAR software, but in some vendors, it does not work with ECG gating. Introduced in 2008, dual-energy CT scanners can generate virtual monoenergetic images (VMIs), which are much less susceptible to metal artifacts than standard CT images. Objective: This study aimed to evaluate if dual-energy CT can reduce metal artifacts caused by ICD leads by using VMIs. The second objective was to determine how the angle between the electrode and the plane of imaging affects the severity of the artifacts in three planes of imaging. Methods: A 3D-printed model was constructed to obtain a 0-90-degree field at 5-degree intervals between the electrode and each of the planes: axial, coronal, and sagittal. This electrode was scanned in dual-energy and single-energy protocols. VMIs with an energy of 40-140 keV with 10 keV intervals were reconstructed. The length of the two most extended artifacts originating from the tip of the electrode and 2 cm above it-at the point where the thick metallic defibrillating portion of the electrode begins-was measured. Results: For the sagittal plane, these observations were similar for both points of the ICDs that were used as the reference location. VMIs with an energy over 80 keV produce images with fewer artifacts than similar images obtained in the single-energy scanning mode. Conclusions: Virtual monoenergetic imaging techniques may reduce streak artifacts arising from ICD electrodes and improve the quality of the image. Increasing the angle of the electrode as well as the imaging plane can reduce artifacts. The angle between the electrode and the beam of X-rays can be increased by tilting the gantry of the scanner or lifting the upper body of the patient.

The objective of this paper is to evaluate the effect of reduced sampling of MRI k-space on the diagnosis of myocarditis with T2 mapping. A MATLAB model of a digital cardiac phantom was altered from a different source to test which scan acceleration methods in terms of k-space sampling were effective. Results indicated that the reduced matrix sampling method allowed for effective diagnosis, much similar to T2 mapping without the implementation of any reduced k-space sampling methods.

In cardiac nuclear medicine examinations, absorption in the body is the main factor in the degradation of the image quality. The Chang and external source methods were used to correct for absorption in the body. However, fundamental studies on attenuation correction for electrocardiogram (ECG)-synchronized CT imaging have not been performed. Therefore, we developed and improved an ECG-synchronized cardiac dynamic phantom and investigated the synchronized time-phase-gated attenuation correction (STPGAC) method using ECG-synchronized SPECT and CT images of the same time phase. Methods: As a basic study, SPECT was performed using synchronized time-phase-gated (STPG) SPECT and non-phase-gated (NPG) SPECT. The attenuation-corrected images were, first, CT images with the same time phase as the ECG waveform of the gated SPECT acquisition (with CT images with the ECG waveform of the CT acquisition as the reference); second, CT images with asynchronous ECG; third, CT images of the 75% region; and fourth, CT images of the 40% region. Results: In the analysis of cardiac function in the phantom experiment, left ventricle ejection fraction (heart rate, 11.5%-13.4%; myocardial wall, 49.8%-55.7%) in the CT images was compared with that in the STPGAC method (heart rate, 11.5%-13.3%; myocardial wall, 49.6%-55.5%), which was closer in value to that of the STPGAC method. In the phantom polar map segment analyses, none of the images showed variability (F (10,10) < 0.5, P = 0.05). All images were correlated (r = 0.824-1.00). Conclusion: In this study, we investigated the STPGAC method using a SPECT/CT system. The STPGAC method showed similar values of cardiac function analysis to the CT images, suggesting that the STPGAC method accurately reconstructed the distribution of blood flow in the myocardial region. However, the target area for attenuation correction of the heart region was smaller than that of the whole body, and changing the gated SPECT conditions and attenuation-corrected images did not affect myocardial blood flow analysis.